Integrated Circuit (IC) modules containing integrated chips mounted on a circuit transposer, also called a carrier, a deck or an interposer, are known in the art. For example, see U.S. Pat. No. 4,074,342, assigned to the assignee of the present invention and incorporated herein by reference. As disclosed in U.S. Pat. No. 4,074,342 and shown in FIG. 1 herein, the chip interposer 30 was externally connected through solder balls 32 on one interposer surface to a substrate 29. Deposited conductors 34 interconnect mounted integrated circuit chips 36 with each other and with the external solder balls 32 through vias 38. The integrated circuit chips are also attached to the interposer by solder balls 42. Module pins 24, which are connected through substrate wiring (not shown) to the interposer, connect the module to the next level of packaging, i.e. to the printed circuit board. These interposers may carry more than one chip and provide interconnections both between the chips mounted thereon and to external package pins. Because of the complexity added to the IC module by including the interposer, these modules are expensive The interposer may be as complex as the module substrate. Consequently, the interposer may cost as much as the substrate and may, therefore, double the module cost.
Besides the added cost of the interposer, the module cost is higher because the addition of the interposer reduces module yield. Since, the interposer, which, typically, is soldered to the substrate, adds module assembly steps, these modules have more opportunities to fail. Assembly failures may occur from a defective part, e.g., the interposer, chip or substrate, or, from faulty solder connections.
Furthermore, good solder connections may fail under normal operating conditions because of non-uniform package thermal expansion or contraction. Normally, the chips themselves are the source of the heat that causes thermal expansion. Since each chip may burn several watts of power, encapsulating several chips mounted on a single interposer quickly leads to a significant amount of heat in the final package. Additionally, since, in some more complex packages, heat is removed directly form the chips, the substrate is cooled through the chips. Thus, when such a package is turned off, the chips cool faster than the substrate, placing additional mechanical stress on the package. Thermal expansion or contraction places mechanical stress on everything in the package. Consequently, the chip or carrier bonds may receive catastrophic stress. In order to maintain chip temperature to within a desired temperature range, the heat generated by the chips in the package must be transferred from the chips to the exterior of the package, and then, dissipated. The more efficient the heat transfer, the narrower the package operating temperature range. The narrower the package operating temperature range, the less the thermal expansion or contraction that occurs.
Non-uniform package temperature further exacerbates stress. One approach to reducing non-uniform temperature related stress in these modules was to make the interposer of a material having the same Temperature Coefficient of Expansion (TCE) as the chips. However, this meant that the interposer was made of the same material and in the same manner as the IC chips. As noted above, making the interposer in the same manner as the substrate kept package cost high.
Heat transfer and power dissipation is important, not only for reliability reasons, but also for newer semiconductor technologies and for superconductors which must operate at liquid nitrogen temperatures or below. These low temperature IC's require fast efficient heat transfer and dissipation. If the junction temperature of a low temperature IC rises too far above the boiling point of liquid nitrogen, the IC will fail. Consequently, very expensive, complicated packages have been required for low temperature applications. These low temperature chip packages are a major portion of the cost of low temperature IC's.